The present invention relates to a power train for an amphibious vehicle, which power train comprises an engine and in-line transmission, with a power take off positoned between the engine and the in-line transmission of the vehicle and commonly known as a sandwich power take off. The invention also relates to an amphibious vehicle comprising such a power train.
In a conventional vehicle power train having an engine and an in-line transmission, an input or primary shaft of the transmission is driven from the flywheel by means of a clutch. Alternatively, where the transmission comprises an automatic gearbox, the input shaft may be driven from a fluid flywheel, known as a torque converter. In known sandwich power take off arrangements, the input shaft of the transmission is extended and a drive means in the form of a sprocket is mounted between the clutch or fluid flywheel and the casing of the transmission. The sprocket drives a power take off by means of a belt or chain.
This known arrangement significantly increases the length of the engine and transmission assembly, and requires fewer sets of bearings to support the input shaft extension in the front of the gearbox, where space is restricted. It is also necessary to cut away the bell housing or gearbox casing to make room for the chain or belt.
It is an object of the invention to provide a power train having a sandwich power take off which can be manufactured with less machining operations and which is more adaptable to various power train layouts than prior art sandwich power take offs.
According to a first aspect of the present invention there is provided a power train for an amphibious vehicle, the power train comprising an engine having a crankshaft and a solid or fluid flywheel, and a transmission arranged generally in-line with the crankshaft of the engine, the transmission having an input shaft driven from the flywheel the power train further comprising a power take off for driving a power take off shaft adapted to drive a marine propulsion means of the vehicle, characterised in that the power take off comprises drive means attached to the flywheel end of the crankshaft, the drive means being adapted to drive the power take off shaft.
In one preferred embodiment, the drive means is provided on a peripheral surface of the flywheel. In this arrangement, the drive means may comprise a set of teeth provided on an outer periphery of the flywheel, the teeth driving the power take off shaft through a chain or toothed belt.
In a further preferred embodiment, the drive means is provided between the flywheel end of the crankshaft and the flywheel. In this arrangement, the drive means may comprise a sprocket which drives the power take off shaft through a chain or toothed belt. The sprocket may be mounted to the end of the crankshaft between the end and the flywheel, and may be held in position by means of fasteners which also attach the flywheel to the crankshaft end. Alternatively, the drive means may comprise a bevel gear mounted on the flywheel end of the crankshaft. The bevel gear mounted on the flywheel end of the crankshaft meshes with a second bevel gear which can be mounted for rotation with the power take off shaft itself or with an intermediate shaft which is adapted to drive the power take off shaft. The intermediate shaft may be adapted to drive the power take off shaft through a constant velocity (CV) or other rotating articulating joint. Alternatively, the intermediate shaft carries a third bevel gear which meshes with a fourth bevel gear mounted for rotation with the power take off shaft.
Where drive is transmitted from the drive means to the power take off shaft via a chain or toothed belt, the chain or toothed belt may be adapted to drive a driven sprocket for driving the power take off shaft. The driven sprocket may be mounted for rotation with the power take off shaft, or, where the engine and transmission are adapted to be mounted transversely to the longitudinal axis of the vehicle, the driven sprocket may be mounted for rotation with an intermediate shaft which is adapted to drive the power take off shaft through a pair of bevel gears.
An intermediate casing may be provided between a bell housing of the transmission and a casing of the engine. The intermediate casing may have an extension which houses the driven sprocket, gears, or CV joint; and the chain, toothed belt, or power take off shaft(s).
Alternatively, a bell housing of the transmission may be adapted to house the driven sprocket and the chain or toothed belt.
A decoupler may be provided in the drive to the marine propulsion unit.
It is a particular advantage of the power train according to the invention, that it is possible to provide full engine power to the marine propulsion means, with a minimum of frictional losses.
According to a second aspect of the invention, there is provided an amphibious vehicle having a power train in accordance with the first aspect of the invention.